In a system for consuming universal multimedia, the adaptive conversion of contents is an important process to provide the best representation method of the contents under a requirement that the adaptive conversion of contents must support various kinds of terminals and various network accesses. The adaptive conversion of contents may be considered from two points of views. One is modality conversion that converts contents from one modality (e.g., video) to another modality (e.g., image). The other is contents transcoding that changes the bit rate (or quality) of contents without converting the modality of the contents. In many theses, the term transcoding is frequently used as the meaning of the modality conversion. However, in the present invention, the two terms are used distinctively as described above for the purpose of clarity. A modality includes not only a mode, such as video, images, graphic images, audio and text, but also coding format, such as MPEG, JPEG and GIF.
It is assumed that a multimedia document formed of multiple contents items is transmitted to a user and consumed in a terminal. To adapt the document to a provided resource restriction (e.g., a total bit rate or a total amount of data), determination related to the Quality of Service (QoS) for modality conversion in a determination engine (104 of FIG. 1) must reflect answers to two basic questions for all the contents items, that is, when the modality conversion should be performed and what the modality of an output contents item is. Especially, answers to the two basic questions, which reflect the preference of the user from the viewpoint of the user, are required.
Without the answers to the two questions, proper modality conversion and contents transcoding technology suitable for adapting contents cannot be applied. Until now, there has been no systematical research capable of simultaneously answering the two basic questions. The determination process of the determination engine 104 for dealing with such questions is first represented by a conventional resource allocation problem as described in a thesis entitled “Adapting Multimedia Internet Contents for Universal Access,” Rakesh Mohan, John R. Smith, and Chung-Sheng Li, “IEEE Trans. Multimedia,” Vol. 1, No. 1, pp. 104-114, March 1999.
Ri and Vi are the resource and contents value of a contents item i in a document, respectively. In this case, the resource of a contents item can be the amount of data or a bit rate, and the contents value designates the amount of information transmitted through the contents. Universally, the Vi is a function that is not reduced with respect to the Ri, and depends on subjective evaluation that varies with persons. The contents value is represented by following Equation.Vi=fi(Ri,Pi,M)  (1)
In Equation 1, the contents value Vi is represented by the function of a resource Ri, modality support capability M, and user preference Pi. In this case, a resource allocation for the contents item i can be represented by the following Equation 2.
                              (                                    ∑              i                        ⁢                                          V                i                            ⁢                                                          ⁢              is              ⁢                                                          ⁢              maximum                                )                ⋀                  (                                                    ∑                i                            ⁢                              R                i                                      ≤                          R              c                                )                ⋀                  (                      satisfaction            ⁢                                                  ⁢            of            ⁢                                                  ⁢            user            ⁢                                                  ⁢            preference                    )                                    (        2        )            
where Λ indicates a logical AND. Equation 2 imports that a condition on the user preference requires that a modality especially desired by the user must be reflected first in the resource allocation. For example, when a sight-impaired person who is weak to the visual representation of information consumes multimedia, an audio modality must be reflected in the resource allocation prior to video, image and text modalities.
A problem arises in that a set of {Ri} satisfying a resource restriction Rc and the condition on the user preference given in Equation 2 should be found. The present invention basically deals with a solution to the problem from the viewpoint of the modality conversion that considers the user preference.
In a conventional access method, a contents value is related with a resource according to a single analyzing function (e.g., logarithm function) or a random curve designated by a producer or a provider. However, a contents value model represented by the single analyzing function cannot exhibit a correlation between contents values existing in other modalities. Especially, a user preference condition cannot be reflected in contents modeling.
Additionally, conventional access methods considering the user preference in contents modality conversion cannot concretely reflect an actual situation. For example, it is assumed that a specific video clip in a server should be converted and transmitted to a terminal, and the terminal supports all the modalities of images, audio and text except for the modality of video. In the early stage of transmission, the bandwidth of a network is sufficient to transmit images, converted from the video, to the terminal. However, if the bandwidth is too narrow to transmit the converted images at the point when time has elapsed, the video needs to be converted into the audio modality that requires a narrower bandwidth. Even, the conversion of the video into text is required. By the above example, it can be clearly understood that modality conversion having a conversion sequence depending on the variable characteristics of a network bandwidth handled by the present invention is necessary.
As another example, it is assumed that a network can transmit all the modalities of video, images, audio and text. There is a possibility that a user changes the terminal thereof while utilizing contents. In the case where the user uses a Personal Digital Assistant (PDA), the PDA is suitable for processing the image modality rather than the video modality and can show most images due to the characteristics thereof, so that the conversion of the video into images is selected. However, if the user changes the terminal from the PDA to a mobile phone, the modality conversion of the video into audio is required. The above-described example shows the necessity of modality conversion that can occur due to the different capabilities of terminals in a session shift.
Actually, it is very difficult that a user predicts the characteristics of a temporary network or inspects the processing capability of a new terminal in a short time. Additionally, the selection of modality conversion is input whenever an important change occurs may cause considerable inconvenience to the user. The conventional methods cannot propose a method of solving the problem on the flexible and clear expression of user preference for the modality conversion. Additionally, conventional research in the resource allocation method focuses only on the contents transcoding, and does not describe when and how the modality conversion is determined, which are two questions for all contents items. Furthermore, the user preference for the modality conversion is not properly dealt with in the research.